The invention relates to a transfer sheet separator for use with an electrophotographic copying machine.
FIG. 1 shows a conventional sheet separator as used in an electrophotographic copying machine. In this Figure, a drum 2 rotating in the direction indicated by an arrow 1 is peripherally provided with a photoconductive, photosensitive member, and an electrostatic latent image is formed thereon by the known electrophotographic process. The latent image is developed by either dry or wet developing process to provide a toner image. A transfer sheet 3 is fed in the direction indicated by an arrow 4 and urged by a charger 5 into abutting engagement against the peripheral surface of the drum 4, whereby the toner image on the periphery of the drum is transferred onto the sheet 3. During the abutting engagement between the sheet and the drum, one lateral edge of the sheet 3 rides on a separation member 6, which separates this lateral edge of the sheet 3 away from the drum surface as the sheet 3 moves forward.
The separation member 6 extends around the drum periphery and also around the periphery of a turn roller 7, and has its opposite ends held by holding means, not shown. The separation member 6 is tensioned so as to be in abutting engagement with the peripheral surface of both the drum 2 and the turn roller 7. The turn roller 7 is fixedly mounted on a shaft 9 which is rotatably mounted on stationary members, and is normally maintained in rotation in the direction indicated by an arrow 8. A plurality of guide rollers 11 are also fixedly mounted on the shaft 9, and rotate in the direction of the arrow 8 together with the turn roller 7.
As one lateral edge of the sheet 3 moves along the separation member 6 into the space between it and the turn roller 7, the sheet 3 will be separated from the drum surface as indicated at 3A. The sheet 3 is held by the turn roller 7 only at its one lateral edge, so that the resilience of the sheet material causes the radius of curvature in the sheet 3 to be increased gradually as further axially removed from the turn roller 7. Consequently, the image carrying surface of the sheet 3 may move into abutment against an upper shield plate 12 or some other stationary member located in the vicinity thereof, causing a jamming or a rubbing of the image. Such effect is considerably pronounced under low humidity condition when the transfer sheet bears an increased amount of electrostatic charge and hence is strongly attracted toward such stationary members. This disadvantage can be eliminated by blowing an air stream, as indicated by an arrow 13, against the sheet 3 on its image carrying side so as to urge the rear surface of the sheet 3 against the guide rollers, or by withdrawing air from the rear surface of the sheet to produce a negative pressure there, again causing the sheet 3 to bear against the peripheral surface of the guide rollers 11. In these instances, one or more fans must be provided, which require the provision of a special space, interfering with the design of a compact copying machine. With a copying machine of wet developing type, the quantity of air stream which is either supplied or withdrawn accelerates the evaporation of the solvent from the drum surface and a developing tank, preventing an efficient use of the solvent. Additionally, the quantity of evaporated solvent may cause a contamination of internal components. With a copying machine of dry developing type, the air stream may disturb the unfixed image on the sheet 3 or may cause a dispersion of a toner powder which is disengaged from the drum surface of the sheet 3 into the space of the machine, thus presenting an additional space requirement to result in an increased cost.